1. Field of the Invention
The present invention relates to a surface acoustic wave resonator using shear horizontal (SH) waves, and more specifically, the present invention relates to a surface acoustic wave resonator in which an interdigital transducer made of a metal containing W or Ta as its main component is provided on a piezoelectric substrate, a filter, a duplexer, and a communication apparatus.
2. Description of the Related Art
Conventionally, a synthesizer local oscillation circuit, which is used for selecting a channel in a portable wireless device having a VHF/UHF band, requires not only miniaturization but also a wider band function for handling the multi-channel system. In addition, even in a surface acoustic wave device used in a voltage-controlled oscillator, which is an essential component of the local oscillator, size reduction and band-widening are strongly demanded.
A surface acoustic wave resonator generating a surface acoustic wave such as a Rayleigh wave is known. In the surface acoustic wave resonator using the Rayleigh wave, however, no matter what type of piezoelectric substrate is used, the electromechanical coupling coefficient is small. Thus, it is difficult to achieve a wider band function.
As a result, a surface acoustic wave resonator using the SH wave has been studied in an attempt to provide a surface acoustic wave resonator having a large electromechanical coupling coefficient so as to achieve the wider band function. A Love wave which is known to be a type of the SH wave is generated by forming an interdigital transducer on the piezoelectric substrate, wherein the interdigital transducer is made of a metal film which has slower sound velocity and a higher density than that of a piezoelectric substrate.
Such a surface acoustic wave resonator, conventionally has a structure in which an interdigital transducer made of Au is formed on a LiNbO.sub.3 substrate of Y-cut X-propagation.
However, since the surface acoustic wave resonator, which uses Au in the interdigital transducer, requires excessive material cost, the surface acoustic wave resonator is very expensive.
Thus, a surface acoustic wave resonator in which a metal containing W or Ta, which is cheaper than Au, as its main component, is used in an interdigital transducer, has been examined.
In general, a surface acoustic wave resonator and a surface wave filter are contained in a ceramic package, and have a structure in which the external terminal of the ceramic package and a bonding pad of an interdigital transducer are connected via wire bonding.
However, when a surface acoustic wave resonator using a metal containing W or Ta as its main component of the interdigital transducer is formed, since the metal having the main component of W or Ta resists being bonded to Au, ball bonding cannot be performed with respect to a wire made of Au or alloys of Au.
Additionally, in order to excite the Love wave, the thickness of an electrode film of the interdigital transducer made of a metal having the main component of W or Ta is set to about 0.02 .mu.m to about 1.0 .mu.m.
When the electrode film of the interdigital transducer made of a metal having the main component of W or Ta has a thickness which is greater than this range, there is a problem which occurs when forming an electrode pattern of the interdigital transducer via reactive ion etching.
In other words, when the electrode pattern is formed of a metal having a main component of W or Ta, a resist is removed before completion of etching of the electrode pattern and thereby, the electrode patterns are damaged.